Showing papers by "University of Alicante published in 2011"

Evolution and classification of the CRISPR-Cas systems

Abstract: The CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated proteins) modules are adaptive immunity systems that are present in many archaea and bacteria. These defence systems are encoded by operons that have an extraordinarily diverse architecture and a high rate of evolution for both the cas genes and the unique spacer content. Here, we provide an updated analysis of the evolutionary relationships between CRISPR-Cas systems and Cas proteins. Three major types of CRISPR-Cas system are delineated, with a further division into several subtypes and a few chimeric variants. Given the complexity of the genomic architectures and the extremely dynamic evolution of the CRISPR-Cas systems, a unified classification of these systems should be based on multiple criteria. Accordingly, we propose a 'polythetic' classification that integrates the phylogenies of the most common cas genes, the sequence and organization of the CRISPR repeats and the architecture of the CRISPR-cas loci.

Potential of Different Enzyme Immobilization Strategies to Improve Enzyme Performance

Abstract: Enzyme biocatalysis plays a very relevant role in the development of many chemical industries, e.g., energy, food or fine chemistry. To achieve this goal, enzyme immobilization is a usual pre-requisite as a solution to get reusable biocatalysts and thus decrease the price of this relatively expensive compound. However, a proper immobilization technique may permit far more than to get a reusable enzyme; it may be used to improve enzyme performance by improving some enzyme limitations: enzyme purity, stability (including the possibility of enzyme reactivation), activity, specificity, selectivity, or inhibitions. Among the diverse immobilization techniques, the use of pre-existing supports to immobilize enzymes (via covalent or physical coupling) and the immobilization without supports [enzyme crosslinked aggregates (CLEAs) or crystals (CLECs)] are the most used or promising ones. This paper intends to give the advantages and disadvantages of the different existing immobilization strategies to solve the different aforementioned enzyme limitations. Moreover, the use of nanoparticles as immobilization supports is achieving an increasing importance, as the nanoparticles versatility increases and becomes more accessible to the researchers. We will also discuss here some of the advantages and drawbacks of these non porous supports compared to conventional porous supports. Although there are no universal optimal solutions for all cases, we will try to give some advice to select the optimal strategy for each particular enzyme and process, considering the enzyme properties, nature of the process and of the substrate. In some occasions the selection will be compulsory, for example due to the nature of the substrate. In other cases the optimal biocatalyst may depend on the company requirements (e.g., volumetric activity, enzyme stability, etc).

Recent advances in Sonogashira reactions

Abstract: The coupling of aryl or vinyl halides with terminal acetylenes catalysed by palladium and other transition metals, commonly termed as Sonogashira cross-coupling reaction, is one of the most important and widely used sp2–sp carbon–carbon bond formation reactions in organic synthesis, frequently employed in the synthesis of natural products, biologically active molecules, heterocycles, molecular electronics, dendrimers and conjugated polymers or nanostructures. This critical review focuses on developments in the Sonogashira reaction achieved in recent years concerning catalysts, reaction conditions and substrates (352 references).

Catalytic routes for the conversion of biomass into liquid hydrocarbon transportation fuels

Abstract: Concerns about diminishing fossil fuel reserves along with global warming effects caused by increasing levels of CO2 in the atmosphere are driving society toward the search for new renewable sources of energy that can substitute for coal, natural gas and petroleum in the current energy system. Lignocellulosic biomass is abundant, and it has the potential to significantly displace petroleum in the production of fuels for the transportation sector. Ethanol, the main biomass-derived fuel used today, has benefited from production by a well-established technology and by partial compatibility with the current transportation infrastructure, leading to the domination of the world biofuel market. However, ethanol suffers from important limitations as a fuel (e.g., low energy density, high solubility in water) than can be overcome by designing strategies to convert non-edible lignocellulosic biomass into liquid hydrocarbon fuels (LHF) chemically similar to those currently used in internal combustion engines. The present review describes the main routes available to carry out such deep chemical transformation (e.g., gasification, pyrolysis, and aqueous-phase catalytic processing), with particular emphasis on those pathways involving aqueous-phase catalytic reactions. These latter catalytic routes achieve the required transformations in biomass-derived molecules with controlled chemistry and high yields, but require pretreatment/hydrolysis steps to overcome the recalcitrance of lignocellulose. To be economically viable, these aqueous-phase routes should be carried out with a small number of reactors and with minimum utilization of external fossil fuel-based hydrogen sources, as illustrated in the examples presented here.

Transformations of biomass-derived platform molecules: from high added-value chemicals to fuels via aqueous-phase processing.

Abstract: Global warming issues and the medium-term depletion of fossil fuel reserves are stimulating researchers around the world to find alternative sources of energy and organic carbon. Biomass is considered by experts the only sustainable source of energy and organic carbon for our industrial society, and it has the potential to displace petroleum in the production of chemicals and liquid transportation fuels. However, the transition from a petroleum-based economy to one based on biomass requires new strategies since the petrochemical technologies, well-developed over the last century, are not valid to process the biomass-derived compounds. Unlike petroleum feedstocks, biomass derived platform molecules possess a high oxygen content that gives them low volatility, high solubility in water, high reactivity and low thermal stability, properties that favour the processing of these resources by catalytic aqueous-phase technologies at moderate temperatures. This tutorial review is aimed at providing a general overview of processes, technologies and challenges that lie ahead for a range of different aqueous-phase transformations of some of the key biomass-derived platform molecules into liquid fuels for the transportation sector and related high added value chemicals.

Ultrasound-Assisted Extraction of Natural Products

Abstract: Ultrasound-assisted extraction (USAE) is an interesting process to obtain high valuable compounds and could contribute to the increase in the value of some food by-products when used as sources of natural compounds. The main benefits will be a more effective extraction, thus saving energy, and also the use of moderate temperatures, which is beneficial for heat-sensitive compounds. For a successful application of the USAE, it is necessary to consider the influence of several process variables, the main ones being the applied ultrasonic power, the frequency, the extraction temperature, the reactor characteristics, and the solvent–sample interaction. The highest extraction rate is usually achieved in the first few minutes, which is the most profitable period. To optimize the process, rate equations and unambiguous process characterization are needed, aspects that have often been lacking.

Coupling Chemical Modification and Immobilization to Improve the Catalytic Performance of Enzymes

Abstract: Chemical modification and immobilization of enzymes have been usually considered unrelated tools to improve biocatalyst features. However, there are many examples where a chemically modified enzyme is finally used in an immobilized form, and that exemplifies how both tools may be complementary resulting in a synergism in the final results. In this review we present some of the strategies that may give that result. For example, the chemical modification of soluble enzymes may be used to improve their immobilization (reinforcing adsorption or improving multipoint covalent attachment), or just to improve enzyme stability and facilitate the selection of the immobilization conditions. Chemical modification of previously immobilized enzymes benefits from solid-phase chemistry due to the nature of enzymes (e.g., prevention of inactivation, aggregation, etc.). The use of different targets for chemical modifications with small molecules or multifunctional polymers are also discussed: intramolecular or intersubunit cross-linking, one-point modification, generation of artificial microenvironments, etc.

Nickel nanoparticles in hydrogen transfer reactions

Abstract: The transfer hydrogenation of organic compounds is a much safer and more environmentally benign process than reduction reactions involving molecular hydrogen, metal hydrides, or dissolving metals. In transfer hydrogenation, 2-propanol is often preferred as the source of hydrogen because it is cheap, easy to remove, and environmentally friendly. This class of transformation has been mostly pursued through the use of expensive noble metals, such as Ru, Pd, and so forth; research involving cheaper catalytically active metals has been relatively neglected.On the other hand, alcohols have recently emerged as desirable alkylating agents, a useful alternative to organic halides, in reactions of hydrogen autotransfer, also known as the “borrowing of hydrogen” methodology. For instance, the α-alkylation of ketones with alcohols is an atom-efficient process that produces water as the only byproduct in the presence of a noble metal catalyst. Hydrogen autotransfer is also successful in the synthesis of amines through...

Thirty years of platinum single crystal electrochemistry

Abstract: The electrochemistry of platinum single crystals is historically reviewed. After a brief revision of historical results dating before the publication of the landmark experiment by J. Clavilier of the flame annealing in 1980, the controversy introduced by this experiment into the surface electrochemistry community is described. Questions about the structure and composition of the platinum surface after the flame annealing and their implications on the characteristic voltammetry of platinum single crystal electrodes were slowly answered in the years that followed the first introduction of this methodology. One of the last questions to be solved was that about the nature of the chemical species responsible for the charge transfer process that leads to the so-called unusual features in the voltammogram. This was solved with the charge displacement experiment. Nowadays, a great deal of knowledge has been gathered about the structure of the interphase between platinum electrodes and electrolytic solutions and also about the electrocatalytic behaviour of platinum surfaces. State-of-the-art information about platinum electrochemistry is provided, with emphasis on results from our group, especially those obtained with a thermodynamic analysis, involving either constant or variable temperatures and with the laser-induced temperature jump method.

Impregnated ruthenium on magnetite as a recyclable catalyst for the N-alkylation of amines, sulfonamides, sulfinamides, and nitroarenes using alcohols as electrophiles by a hydrogen autotransfer process.

Abstract: Various impregnated metallic salts on magnetite have been prepared, including cobalt, nickel, copper, ruthenium, and palladium salts, as well as a bimetallic palladium–copper derivative. Impregnated ruthenium catalyst is a versatile, inexpensive, and simple system for the selective N-monoalkylation of amino derivatives with poor nucleophilic character, such as aromatic and heteroaromatic amines, sulfonamides, sulfinamides, and nitroarenes, using in all cases alcohols as the initial source of the electrophile, through a hydrogen autotransfer process. In the case of sulfinamides, this is the first time that these amino compounds have been alkylated following this strategy, allowing the use of chiral sulfinamides and secondary alcohols to give the alkylated compound with a diastereomeric ratio of 92:8. In these cases, after alkylation, a simple acid deprotection gave the expected primary amines in good yields. The ruthenium catalyst is quite sensitive, and small modifications of the reaction medium can chang...

Entrepreneurial intentions, motivations and barriers: Differences among American, Asian and European students

Abstract: Should entrepreneurship education be the same in every country or should it be adapted to each context? In addition to answering this question, it appears to be important to identify the concerns students have regarding their entrepreneurship education programs, so as to strengthen their perceptions of feasibility and desirability of an entrepreneurial career. In this article we examine whether differences exist among American, Asian and European students in terms of entrepreneurial intentions and dispositions, as well as motivations and perceived barriers for business startup. Results indicate that entrepreneurial disposition and intentions differ by country but that students across countries are motivated and/or discouraged by similar variables. However, our results indicate that the levels of sensitivity to each motivator and barrier differ by country. Our results support the argument made by past researches that cultural differences should be taken into consideration when developing entrepreneurship education programs.

Quality of life in people with venous leg ulcers: an integrative review.

Abstract: gonzalez-consuegra r.v. & verdu j. (2011) Quality of life in people with venous leg ulcers: an integrative review. Journal of Advanced Nursing67(5), 926–944. Abstract Objective. To explore the impact of venous leg ulcers on health-related quality of life and analyse the quality of life instruments that have been used for this topic. Background. Venous leg ulcers represent more than 80% of all chronic leg ulcers. Several studies have demonstrated that health-related quality of life is affected in patients with such lesions. Method. An integrative review was conducted, together with an additional methodological review of quality of life instruments. Eight electronic databases were searched, and all studies published between 2003 and 2008 were considered in with both qualitative and quantitative approaches and in Spanish, English, French, German and Portuguese. Thus, no restrictions were applied as regards study design. Results. Twenty-two studies were included; one used mixed methods, three employed qualitative methods and the remaining articles used a quantitative approach. Pain was the factor most frequently identified as affecting health-related quality of life. The generic instruments most commonly used were Short Form-36 and adaptations, the Nottingham Health Profile and EuroQol-5, whilst the disease-specific tools were Hyland, Cardiff Wound Impact Schedule and Charing Cross Venous Leg Ulcer Questionnaire. Two new instruments were also identified, venous leg ulcer quality of life and Sheffield Preference-based Venous Leg Ulcer 5D. Conclusions. The negative impact of venous leg ulcers on health-related quality of life is confirmed in this review. This impact has been measured using a variety of specific health-related quality of life instruments. However, the review findings suggest that the Charing Cross Venous Leg Ulcer Questionnaire is the most appropriate instrument due to its disease-specific psychometric characteristics.

Hands-on experiences of undergraduate students in Automatics and Robotics using a virtual and remote laboratory

Abstract: Automatics and Robotics subjects are always greatly improved when classroom teaching is supported by adequate laboratory courses and experiments following the ''learning by doing'' paradigm, which provides students a deep understanding of theoretical lessons. However, expensive equipment and limited time prevent teachers having sufficient educational platforms, and several low cost and flexible solutions have been developed to permit an effective teaching in Automatics and Robotics at a reasonable cost. Virtual and remote laboratories are inside this group of solutions as Web-based experimentation tools which have demonstrated the importance and effectiveness of hand-on experiences. This paper presents an experience teaching based on a blended-learning method using as experimentation tool a virtual and remote robotic laboratory called RobUALab, which is also described in the paper, in Automatics and Robotics subjects of the Computer Science degree at the University of Alicante. Students experiment with a set of hand-on exercises about Automatics and Robotics using RobUALab, firstly in face-to-face classes where they experiment in-situ with the real plant and, afterwards, they access to the experimentation environment in order to finish remotely their practical exercises outside the laboratory. The results obtained in the evaluation of the educational methodology proposed attest its efficiency in terms of learning degree and performance of the students.

Does Grade Retention Affect Achievement? Some Evidence from PISA

Abstract: Grade retention practices are at the forefront of the educational debate. In this paper, we use PISA 2009 data for Spain to measure the effect of grade retention on students' achievement. One important problem when analyzing this question is that school outcomes and the propensity to repeat a grade are likely to be determined simultaneously. We address this problem by estimating a Switching Regression Model. We find that grade retention has a negative impact on educational outcomes, but we confi rm the importance of endogenous selection, which makes observed differences between repeaters and non-repeaters appear 14.6% lower than they actually are. The effect on PISA scores of repeating is much smaller (-10% of non-repeaters' average) than the counterfactual reduction that non-repeaters would suffer had they been retained as repeaters (-24% of their average). Furthermore, those who repeated a grade during primary education suffered more than those who repeated a grade of secondary school, although the effect of repeating at both times is, as expected, much larger.

Arbuscular Mycorrhizal Fungi (AMF) Improved Growth and Nutritional Quality of Greenhouse-Grown Lettuce

Abstract: Lettuce can be associated with arbuscular mycorrhizal fungi (AMF). This symbiosis involves a molecular dialogue between fungus and plant that includes the activation of antioxidant, phenylpropanoid, or carotenoid pathways. The objective of this study was to test if the association of lettuce with AMF benefited plant growth and increased the contents of compounds potentially beneficial for human health. Results showed that AMF improved growth of lettuce, thus producing a dilution effect on the concentrations of some mineral nutrients (e.g., Ca and Mn). However, Cu, Fe, anthocyanins, carotenoids, and, to a lesser extent, phenolics appeared in higher concentrations (on a wet basis) in mycorrhizal than in nonmycorrhizal plants.

The skewness of science in 219 sub-fields and a number of aggregates

Abstract: This paper studies evidence from Thomson Scientific (TS) about the citation process of 3.7 million articles published in the period 1998---2002 in 219 Web of Science (WoS) categories, or sub-fields. Reference and citation distributions have very different characteristics across sub-fields. However, when analyzed with the Characteristic Scores and Scales (CSS) technique, which is replication and scale invariant, the shape of these distributions over three broad categories of articles appears strikingly similar. Reference distributions are mildly skewed, but citation distributions with a 5-year citation window are highly skewed: the mean is 20 points above the median, while 9---10% of all articles in the upper tail account for about 44% of all citations. The aggregation of sub-fields into disciplines and fields according to several aggregation schemes preserve this feature of citation distributions. It should be noted that when we look into subsets of articles within the lower and upper tails of citation distributions the universality partially breaks down. On the other hand, for 140 of the 219 sub-fields the existence of a power law cannot be rejected. However, contrary to what is generally believed, at the sub-field level the scaling parameter is above 3.5 most of the time, and power laws are relatively small: on average, they represent 2% of all articles and account for 13.5% of all citations. The results of the aggregation into disciplines and fields reveal that power law algebra is a subtle phenomenon.

Shape dependent electrocatalysis

Abstract: In this paper we will review the state-of-the-art in the application of shape-controlled metal nanoparticles in Electrocatalysis, especially in reactions of interest in PEMFCs such as O2reduction and CO, methanol, ethanol and formic acid electrooxidations. In particular, we will focus our attention on shape-controlled platinum (Pt), gold (Au) and palladium (Pd) nanoparticles. In addition, electrocatalytic applications of shape-controlled Pt-based alloy nanoparticles will be also reviewed. The results reported will highlight how important can be controlling the shape of the nanocatalyst and how effective this parameter may be to improve the activity and thus, develop highly active electrocatalysts.

Do drivers matter for the benefits of ISO 14001

Abstract: Purpose – The ISO 14001 is already a global meta‐standard for implementing Environmental Management Systems. The purpose of this paper is to analyze the influence of the sources of motivation that lead companies to adopt this global standard for its perceived benefits.Design/methodology/approach – An extensive review of the academic literature published on ISO 14001, motivations, and benefits has been carried out in order to establish the working hypotheses that are analyzed based on the information obtained from 214 Spanish companies that participated in a survey.Findings – The internal drivers to implement and certify the ISO 14001 standard have a degree of influence on the benefits that is significantly higher than external ones, irrespective of the size of the company and the sector of activity.Practical implications – The findings help to characterize ISO 14001 certified firms and anticipate benefits of the implementation and certification of the standard.Originality/value – The article sheds light o...

The Use and Added Value of Mixed Methods in Management Research

Abstract: The prevalence, characteristics, and added value of mixed methods articles published in two management fields are examined through a sequential mixed methods design with four phases. The results show that mixed methods articles are published in management journals with different prevalence rates and characteristics. Moreover, an analysis of the impact and added value of mixed methods to the field of management is carried out. Implications for scholars, academic institutions, and journals with regard to the application and publication of mixed methods research are examined.

Click chemistry from organic halides, diazonium salts and anilines in water catalysed by copper nanoparticles on activated carbon

Abstract: An easy-to-prepare, reusable and versatile catalyst consisting of oxidised copper nanoparticles on activated carbon has been fully characterised and found to effectively promote the multicomponent synthesis of 1,2,3-triazoles from organic halides, diazonium salts, and aromatic amines in water at a low copper loading.

Multicomponent click synthesis of 1,2,3-triazoles from epoxides in water catalyzed by copper nanoparticles on activated carbon.

Abstract: Copper nanoparticles on activated carbon have been found to effectively catalyze the multicomponent synthesis of β-hydroxy-1,2,3-triazoles from a variety of epoxides and alkynes in water. The catalyst is easy to prepare, reusable at a low copper loading (0.5 mol %), and exhibits higher catalytic activity than some commercially available copper sources. The regio- and stereochemistry of the reaction has been revised and unequivocally established on the basis of X-ray crystallographic analyses. An NMR experiment has been implemented for the rapid and unmistakable determination of the regiochemistry of the process. Some mechanistic aspects of the reaction have been also undertaken which unveil the participation of copper(I) acetylides.

Transition-metal-free O-, S-, and N-arylation of alcohols, thiols, amides, amines, and related heterocycles.

Abstract: A new protocol for the Ullmann-type arylation process of different aromatic heterocycles without any transition-metal catalyst, implying the use of a combination of an excess of potassium hydroxide and dimethyl sulfoxide, is described. The reaction can be performed between a broad range of starting nucleophiles including phenol, alcohols, amines, nitrogen-containing five-membered systems such as pyrazoles, imidazoles, and indoles, and amides with haloarenes, iodide and bromide derivatives giving the best results, the possible pathway involving the in situ generation of the corresponding benzyne intermediate. When the reaction was performed with 2-iodoaniline and either carboxamides or isothiocyanato derivatives, the corresponding benzoazole derivatives were obtained.

Astrophysical Parameters of LS 2883 and Implications for the PSR B1259-63 Gamma-ray Binary

Abstract: This research is partially supported by the Spanish MICINN (grants FPA2010-22056-C06-02, AYA2008-06166-C03-01/03, AYA2010-21697-C05-04/05, and CSD2006-70 and FEDER funds); and by the Generalitat Valenciana (ACOMP/2009/164) and Gobierno de Canarias (ProID2010119). M.R. acknowledges financial support from MICINN and European Social Funds through a Ramon y Cajal fellowship.